The base of R.O.B. contains the other significant circuit board. To access, carefully remove the four screws on the bottom plate. This allows you to see the main circuit board (from the bottom).
Going further, you can carefully remove the four screws holding on the circuit board to flip it over.
The Sharp IR2C25 chips are undocumented motor control drivers. The RFC-CPU10 is a custom Nintendo microcontroller or programmable chip that is also undocumented. The 6 wire rainbow wiring harness goes to the midsection via a coiled cable. The 4 wire white harness leads to the head section. The slide switch disconnects the battery power from the rest of the circuitry when in the off position.
A partial schematic is shown below. Some of the passive components have been left off, most of them support the CPU chip.
R.O.B. uses three motors to move: one in the base and two in the mid-section. Each motor is controlled by a Sharp IR2C25 driver chip. The CPU takes commands from the white wiring harness wire S connected to pin 1. Then the CPU will connect the appropriate output pin connected to A, B, C, D, E, F, or Z. If you take a wire connected to the positive battery terminal and connect it to one of those connection points noted in the diagram, you will get that function to activate. BUT BE CAREFUL, the limit switches are not communicating to you to stop the movement like the CPU controlling it. If you have a gear issue, you'll have to research the repair - links are here, via Google.
An experienced tinkerer/Maker could use this to build controls to make R.O.B. move. It's not as elegant as using the control signals used earlier and it could damage R.O.B. if you are not careful or you do not take the limitations of movement into account.